1. Field of the Invention
The invention relates generally to apparatus and methods for handling photosensitive sheet materials such as photographic film in photocomposition; more particularly, the invention relates to apparatus and methods for accurately controlling the lateral position of the photosensitive material before, during and after its passage through the exposure zone at which character images are formed. The invention further relates to a film take-up mechanism and method to facilitate loading relatively large amounts of exposed film into removable cassettes.
2. Prior Art
In the present state of the art, photographic film or paper handling systems for phototypesetters generally include a driving mechanism comprised of pinch rollers to pull the film out of a supply roll through a flat "exposure window" where the film, during the formation of character images, is held in the focal plane with adequate accuracy. A typical prior system such as that shown in U.S. Pat. No. 3,016,209 uses a fixed locating pad on which the film is held by a spring loaded pressure plate.
Some of the problems encountered in prior art devices are the following:
Difficulty of moving the film forwardly and backwardly repetitively for forward and reverse leading (line spacing), for example, in the composition of columns, tables and the like, along an accurate and repetitive path and without excessive scratching or wear on the film.
Difficulty of laterally guiding the film during machine operation to avoid a wavering left hand margin. If the mechanism is provided with edge guides, the film has a tendency either to wander away from the guides, or to climb over the guides and create a film jam because the lateral force required to move the film laterally away from the guide is too great because of the friction of the pinch roller which is necessary for accurate leading (line spacing).
Difficulty of loading relatively large amounts of exposed film into the output cassette. This is believed to be caused by tension created by the winding mechanism which prevents the newly-wound film from freely taking its natural position around the winding core within the cassette. The result is "film jams" or "bunching" of the film.